Field of the Invention
The present invention relates to an image processing apparatus and an image processing method that can correct a color of an image to be output from a printer, and a program for generating image processing parameters.
Description of the Related Art
The recent improvement in performance of electrophotographic apparatuses can realize high image quality comparable to that of a printing machine. However, the instability of each electrophotographic apparatus, which is peculiar thereto, tends to cause a color variation that is larger than that of a printing machine.
In general, a “single-color” calibration technique is conventionally installed in an electrophotographic apparatus. The “single-color” calibration technique includes generating a look-up table (LUT) usable to correct one-dimensional gradation characteristics corresponding to each of cyan, magenta, yellow, and black (hereinafter, simply referred to as C, M, Y, and K) toners. The LUT is a table that indicates output data corresponding to respective input data segmented at specific intervals. Using the LUT is useful in expressing nonlinear characteristics to which no calculation formula is applicable. Further, the “single-color” is a color that is reproducible using a single toner of C, M, Y, or K. Performing the single-color calibration is useful to correct single-color reproduction characteristics, such as a maximum density and a gradation.
As discussed in Japanese Patent Application Laid-Open No. 2011-254350, a “multi-color” calibration technique using a four-dimensional LUT is conventionally proposed. The “multi-color” is a composite color that is reproducible using a plurality of toners of red, green, and blue or gray (based on CMY). Especially, according to the electrophotography, even when a one-dimensional LUT is used to correct single-color gradation characteristics, a nonlinear difference tends to occur if a plurality of toners is used to express a “multi-color.” Performing the multi-color calibration in such a case is useful to correct multi-color reproduction characteristics which can be expressed by a combination (e.g., a superposition) of a plurality of color toners.
A processing procedure of the calibration including a “multi-color” calibration is described below. First, patches are printed on a recording medium, such as a sheet of paper, based on single-color chart data that is usable to perform the “single-color” calibration. Then, the printed patches are read by a scanner or a sensor. The read patch data is compared with target values having been set beforehand, and a one-dimensional LUT is generated which is used to correct differences between read patch data and the target values. Then, patches are printed on a recording medium based on multi-color chart data that reflects the obtained one-dimensional LUT to perform the “multi-color” calibration, and the printed patches are read by the scanner or the sensor. Further, the read patch data is compared with target values having been set beforehand, and a four-dimensional LUT is generated which is used to correct differences between read patch data and the target values.
As described above, it is feasible to realize highly accurate correction by performing the “multi-color” calibration in such a way as to correct multi-color characteristics that cannot be corrected by the “single-color” calibration.
In addition, it is desirable to start the processing from the “single-color” calibration and then perform the “multi-color” calibration, as described above. However, a significantly long processing time is required to complete both the single-color calibration and the multi-color calibration. For example, in a case of a user who frequently performs single-color printing, there is a higher possibility of performing the single-color calibration because the “multi-color” print is not performed so often. In addition, in an electrophotographic apparatus, there is a tendency that a nonlinear difference occurs in a case of “multi-color” processing as compared with a case of “single-color” processing. Therefore, “multi-color” characteristics may not be sufficiently corrected even in a case where “single-color” characteristics are sufficiently corrected. Accordingly, in a case of a user who frequently performs “multi-color” (e.g., photograph) printing, there is a higher possibility of performing the multi-color calibration rather than performing the single-color calibration.
In response to above-described users' demands, there is a mechanism which provides two buttons independently to enable a user to select each of the single-color calibration and the multi-color calibration and independently perform the selected calibration (see Fuji Xerox technical report NO. 19 2010).
However, according to the above-described technique discussed in Fuji Xerox technical report NO. 19 2010, the single-color calibration and the multi-color calibration are processing to be independently performed. Therefore, if only one of two calibrations is chiefly performed (too often), there is a possibility that the correction accuracy of the calibration may deteriorate.